Cable Size Calculator
Estimate a preliminary conductor size using load current and voltage-drop criteria, then verify it against actual cable ampacity tables.
How this calculator works
When load power is entered, current is estimated as:
3 phase: I = kW × 1000 / (sqrt(3) × V × PF × efficiency).
1 phase: I = kW × 1000 / (V × PF × efficiency).
Two preliminary areas are calculated: one from the editable current-density assumption and one from resistive voltage drop. The calculator selects the next standard conductor size above the larger area.
Voltage-drop estimate uses conductor resistivity adjusted approximately for operating temperature. Cable reactance is not included in this quick size screen.
Example
For a long feeder, voltage drop may require a larger cable even when the current-only screen suggests a smaller conductor.
Source and engineering note
BIS lists IS 732:2019 as the Code of Practice for Electrical Wiring Installations and IS 8130:2013 for conductors used in insulated electric cables and flexible cords. IEC 60364-5-52 covers selection and erection of wiring systems, including current-carrying capacity and voltage drop.
CalcSetu's cable tools are preliminary engineering estimates. Final cable selection must be verified against the actual cable manufacturer's current-carrying-capacity table, installation method, ambient temperature, grouping, harmonics, protective device and short-circuit withstand.
Bureau of Indian Standards - IEC 60364-5-52
Last reviewed: 27 August 2026.
Frequently asked questions
Is the recommended cable size final?
No. It is a preliminary estimate. Final sizing must be checked against manufacturer ampacity tables, derating factors, short-circuit duty and protection.
Why is current density editable?
A single current-density value is not a code ampacity rule. It is only a screening assumption, so CalcSetu makes it visible and editable.
Does the voltage-drop calculation include cable reactance?
No. This quick screen uses a resistive estimate. For larger AC cables and long feeders, use manufacturer R and X data or a detailed electrical design.
Why do installation method and grouping matter?
They change the cable's ability to dissipate heat and therefore its allowable current.